Counterfactual history asks: what if a key event had not occurred? It is one of the most debated methods in historical study. Critics dismiss it as speculation. Defenders argue it is essential for understanding causation — because the only way to test whether an event was truly a cause is to imagine what would have happened without it.

Your case study: What if Archduke Franz Ferdinand had not been assassinated on 28 June 1914? Would World War One still have occurred?

This thought experiment forces you to distinguish between necessary causes (without which the event could not have happened) and sufficient causes (which made the event likely to happen anyway). Understanding this distinction is crucial for A-Level causal analysis.